[user104658]

Unless he was in severe and unresolvable pain then calling it a mercy killing is entirely wrong, in my opinion. I'm trying to give the benefit of the doubt and think that perhaps they both were entirely lacking in support and has been failed by those around her/the care system and she's suffered an acute psychotic episode and done something, which would explain immediately turning herself in.

I say I'm "trying to" give the benefit of the doubt because as the parent of a disabled child this makes me feel really ****ing ill. "Mercy killing" someone with no capacity to speak for themself who is entirely reliant on you for support and advocacy is no excuse at all.